访问外部信息的 DDD 方法 [英] DDD Approach to Access External Information

问题描述

我有一个现有的银行应用程序类，如下所示.银行账户可以是 SavingsBankAccount 或 FixedBankAccount.有一个名为 IssueLumpSumInterest 的操作.对于 FixedBankAccount，只有在账户所有者没有其他账户时才需要更新余额.

I have an existing bank application classes as shown below. The banks account can be of SavingsBankAccount or FixedBankAccount. There is an operation called IssueLumpSumInterest. For FixedBankAccount, the balance need to be updated only if the owner of the account has no other account.

这要求 FixedBankAccount 对象了解帐户所有者的其他帐户.如何通过遵循 SOLID/DDD/GRASP/Information Expert 模式来做到这一点?

This demands the FixedBankAccount object to know about other accounts of the account owner. How to do this by following SOLID/DDD/GRASP/Information Expert pattern?

namespace ApplicationServiceForBank
{

public class BankAccountService
{
    RepositoryLayer.IRepository<RepositoryLayer.BankAccount> accountRepository;
    ApplicationServiceForBank.IBankAccountFactory bankFactory;

    public BankAccountService(RepositoryLayer.IRepository<RepositoryLayer.BankAccount> repo, IBankAccountFactory bankFact)
    {
        accountRepository = repo;
        bankFactory = bankFact;
    }

    public void IssueLumpSumInterest(int acccountID)
    {
        RepositoryLayer.BankAccount oneOfRepositroyAccounts = accountRepository.FindByID(p => p.BankAccountID == acccountID);

        int ownerID = (int) oneOfRepositroyAccounts.AccountOwnerID;
        IEnumerable<RepositoryLayer.BankAccount> accountsForUser = accountRepository.FindAll(p => p.BankUser.UserID == ownerID);

        DomainObjectsForBank.IBankAccount domainBankAccountObj = bankFactory.CreateAccount(oneOfRepositroyAccounts);

        if (domainBankAccountObj != null)
        {
            domainBankAccountObj.BankAccountID = oneOfRepositroyAccounts.BankAccountID;
            domainBankAccountObj.AddInterest();

            this.accountRepository.UpdateChangesByAttach(oneOfRepositroyAccounts);
            //oneOfRepositroyAccounts.Balance = domainBankAccountObj.Balance;
            this.accountRepository.SubmitChanges();
        }
    }
}

public interface IBankAccountFactory
{
    DomainObjectsForBank.IBankAccount CreateAccount(RepositoryLayer.BankAccount repositroyAccount);
}

public class MySimpleBankAccountFactory : IBankAccountFactory
{
    public DomainObjectsForBank.IBankAccount CreateAccount(RepositoryLayer.BankAccount repositroyAccount)
    {
        DomainObjectsForBank.IBankAccount acc = null;

        if (String.Equals(repositroyAccount.AccountType, "Fixed"))
        {
            acc = new DomainObjectsForBank.FixedBankAccount();
        }

        if (String.Equals(repositroyAccount.AccountType, "Savings"))
        {
            //acc = new DomainObjectsForBank.SavingsBankAccount();
        }

        return acc;
    }
}

}

namespace DomainObjectsForBank
{

public interface IBankAccount
{
    int BankAccountID { get; set; }
    double Balance { get; set; }
    string AccountStatus { get; set; }
    void FreezeAccount();
    void AddInterest();
}

public class FixedBankAccount : IBankAccount
{
    public int BankAccountID { get; set; }
    public string AccountStatus { get; set; }
    public double Balance { get; set; }

    public void FreezeAccount()
    {
        AccountStatus = "Frozen";
    }

    public void AddInterest()
    {
        //TO DO: Balance need to be updated only if the person has no other accounts.
        Balance = Balance + (Balance * 0.1);
    }
}

}

阅读

1. 使用 Composition 表示is – a"的问题关系

实现业务逻辑(LINQ to SQL)http://msdn.microsoft.com/en-us/library/bb882671.aspx

Implementing Business Logic (LINQ to SQL) http://msdn.microsoft.com/en-us/library/bb882671.aspx

构建 LINQ to SQL 应用程序

Architecting LINQ to SQL applications

使用 LINQ to SQL 探索 N 层架构http://randolphcabral.wordpress.com/2008/05/08/exploring-n-tier-architecture-with-linq-to-sql-part-3-of-n/

Exploring N-Tier Architecture with LINQ to SQL http://randolphcabral.wordpress.com/2008/05/08/exploring-n-tier-architecture-with-linq-to-sql-part-3-of-n/

DTO (linq2sql) 和 Class 对象之间的混淆！

域驱动设计(Linq to SQL) - 如何删除聚合的部分内容?

推荐答案

通过阅读您的要求，我会这样做:

From reading your requirement, here is how I would do it:

//Application Service - consumed by UI
public class AccountService : IAccountService
{
    private readonly IAccountRepository _accountRepository;
    private readonly ICustomerRepository _customerRepository;

    public ApplicationService(IAccountRepository accountRepository, ICustomerRepository customerRepository)
    {
        _accountRepository = accountRepository;
        _customerRepository = customerRepository;
    }

    public void IssueLumpSumInterestToAccount(Guid accountId)
    {
        using (IUnitOfWork unitOfWork = UnitOfWorkFactory.Create())
        {
            Account account = _accountRepository.GetById(accountId);
            Customer customer = _customerRepository.GetById(account.CustomerId);

            account.IssueLumpSumOfInterest(customer);

            _accountRepository.Save(account);
        }
    }
}

public class Customer
{
    private List<Guid> _accountIds;

    public IEnumerable<Guid> AccountIds
    {
        get { return _accountIds.AsReadOnly();}
    }
}

public abstract class Account
{
    public abstract void IssueLumpSumOfInterest(Customer customer);
}

public class FixedAccount : Account
{
    public override void  IssueLumpSumOfInterest(Customer customer)
    {
        if (customer.AccountIds.Any(id => id != this._accountId))
            throw new Exception("Lump Sum cannot be issued to fixed accounts where the customer has other accounts");

        //Code to issue interest here
    }
}   

public class SavingsAccount : Account
{
    public override void  IssueLumpSumOfInterest(Customer customer)
    {
        //Code to issue interest here
    }
}

1. 帐户汇总上的 IssueLumpSumOfInterest 方法需要客户汇总来帮助决定是否应发放利息.
2. 客户汇总包含帐户 ID 列表 - 不是帐户汇总列表.
3. 基类Account"具有多态方法 - FixedAccount 检查客户没有任何其他帐户 - SavingsAccount 不执行此检查.

1. The IssueLumpSumOfInterest method on the Account aggregate requires the Customer aggregate to help decide whether interest should be issued.
2. The customer aggregate contains a list of account IDs - NOT a list of account aggregates.
3. The base class 'Account' has a polymorphic method - the FixedAccount checks that the customer doesn't have any other accounts - the SavingsAccount doesn't do this check.

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